Dyeing of aluminum and/or aluminum alloys



United States Patent Of 2,989,427 DYEING F ALUMINUM AND/ OR ALUMINUM ALLOYS Joseph D. Noonan, Lancaster, N.Y., and James E. Loughlin, New Milford, N.J., assignors to Allied Chemical Corporation, New York, N.Y., a corporation of New York No Drawing Filed Apr. 8, 1959, Ser. No. 804,885 j Y 7 Claims. (Cl. 1486.2)

This invention relates to the formation of colored coatings on aluminum and/ or aluminum alloys and to such colored aluminum and/or'aluminum alloys. More particularly this invention relates to thedyeing of chemical coated aluminum and/or aluminum alloys and to the resultant dyed chemical coated aluminum and/ or aluminum alloys.

Electrochemical and chemical treatments of the surface of aluminum and its alloys to form an integral inorganic film or coating are well known. Of the electrochemical treatments, anodizing is the best known and most widely used. It is, however, a more costly treatment than the chemical treatments such as the well known phosphate and chromate coating procedures. These chemical coating procedures, however, result in coatings which either because of their thinness or softness, or both, or for other reasons, can not, by heretofore known techniques, be dyed satisfactorily. i

It is among the objects of the present invention to provide a process of dyeing chromate coated aluminum and/ or aluminum alloys.

It is another object to provide such process resulting in a dyed chromate coating which is not deleteriously affected with respect to its wear and corrosion resistant properties.

It is still another object of this invention to provide a dyed chromate coated aluminum or aluminum alloy of desired uniform shade integrally formed with the coating and which dye does not deleteriously affect the wear and corrosion resistant properties of the chromate coating.

Other objects and advantages of the present invention will be apparent from the following detailed description thereof.

In accordance with this invention, the aluminum or aluminum alloy in any desired form, including plates, bars, rods, etc., or other articles, is given a chromate coat ing by treatment with a chromate coating solution containing a lake-forming substrate so that this substrate is dispersed throughout the chromate coating and the thus coated metal is then dyed with a cationic dye, otherwise known as a basic dye. The insoluble lake of the dyestuif is thus produced within and on the chromate coating, integral therewith, and of much deeper and more attractive shade than has heretofore been obtainable on chemical coated aluminum.

In practicing this invention, the metal (aluminum or its alloys) piece or pieces are first cleaned, for example by dipping in hot 85% phosphoric acid, and the clean pieces then immersed in the chromate coating bath containing the lake-forming substrate. The amount of the lakeforming substrate used can be varied; it is possible to use from about 0.1% to about 5% by Weight, preferably from about 0.2% to about 3% by weight, based on the weight of the chromating solution. While it is preferred to apply the chromate coating containing the lake-forming substrate by dipping the metal article in a bath of the chromating solution, it will be appreciated this invention is not limited to this mode of application and includes other procedures, such as spray procedures, for forming the chromate coating containing the lake-forming substrate uniformly distributed therethroughou-t.

Commercially available chromating solutions used for "ice forming chromate coatings on aluminumor its alloys, modified in accordance with the present invention to contain the lake-forming substrate, may be employed in the practice of this invention. For example, the chromate coatings disclosed in United States Patents 2,796,370 and 2,796,371 may be employed. These patents disclose chromate coating compositionscontainingchromic acid or-a water soluble salt (e.g. sodium or potassium). thereof along with an inorganic acid, ferricyanic acid, ferrocyanic acid, mixtures of such acids, water soluble salts (e.g. sodium or potassium) of such acids and fluorine compounds. The concentration of chromic acid in the chromate coating solution may be from 0.5 gram per liter to grams per liter. The concentration of alkali metal ferricyanide or ferrocyanide may be from 0.1 gram per liter to 50 grams per liter. Hydrofluoric acid,.if used, may be used in a concentration of from 0.005 to 5 grams per liter. An equivalent amount of a salt of hydrofluoric acid such as barium, sodium, potassium or ammonium fluorides may beused. As indicated, instead of chrornic acid; salts thereof, such as sodium or potassium chromateor bichromate, with an inorganic acid, such as sulfuric, nitric or hydrofluoric acid, may be used. Instead of the hydrofluoric acid or salts thereof, fluosilicic acid or fluoboric acid, or salts thereof such as the sodium, potassium, ammonium and barium salts, may be employed. The concentration of fluosilicic acid may vary from 0.075 to 8 grams per liter, andof the fluoboric acid from 3.3 to 33 grams per liter. Salts of these acids are used in amounts chemically equivalent to the indicated amount of acid.

Good results have been obtained using a solution containing about 2.5% by weight ofpot-ass ium' ferrocyanide, about 0.5% sodium fluoride, about 0.1% chromicoxide (CrO and about 96% water, to which chromating solution about 0.3% lake-forming substrate is added.

The chromate coating solution (the expression chromate is used herein in a broad sense and includes the solutions hereinabove described containing chrornic acid as well as such solutions containing chromate or bichromate salts along with a mineral acid) is applied to the aluminum, or alloy containing aluminum as a major constituent, at a temperature between 35 and 160 F. desirably by immersing the aluminum or aluminum alloy in the chromate coating solution for from. about 5-10 seeonds to 10 minutes or longer.

The particular lake forming substrate used depends chiefly on the dyestufl applied. Examples of lake-forming substrate which can be used are the heteropolyacids such as phosphotungstic acid, phosphomolybdic acid and mixtures thereof; tannin; sulfonated naphthalene condensate (Naccotan A); tantar-emetic; rosin soap precipitates; condensation products of trichlorobenzyl chloride and sulfonated phenols (Katanols); formaldehyde naphthalene sulfonic acid condensation products (Tamol NNO); and mixtures of such lake-forming materials. I i 7 Any cationic dyestufi or mixture thereof capable of forming a water-insoluble lake with the lake-forming substrate can be used to effect the dyeing. As typical of such dyestuifs, the following are mentioned:

Victoria Green WB, CI. 42000 lBismarck Brown 53, 0.1. 21010 Methylene Blue 2B, C.I. 52015 Auramine 0 (yellow), C1. 4100 Malachite Green, CI. 42000 Rhoduline Blue 6G, CI. 42025 Victoria Pure Blue B0, CI. 42595 Rhodamine B, CI. 45170 Rhodamine 6G, Cl. 45

Thioflavine T, Cl. 49005 Indolium styryl dyes of the type disclosed in United States Patent 2,7 34,901. I

G i \CHI O CH;

Blue Dye, Example 3 of British Patent 807,241, having the formula:

Blue Dye, Example 4 of United States Patent 2,716,655, having the formula:

(I) NH;

CH; 4-/ O NH-CHICHI.OHLNCHI 804C115 Reddish Brown Dye, Example 6 of the British Patent 807,241, having the formula:

f) N H;

OH: I CHr-IlT-CHzCHz. CHzHN 0 C BENCH:

Yellow Dye, Example 11 of the United States Patent 2,155,459, having the formula:

Red Dye, CI. 48015, Example 7 of United States Patent 2,179,895, having the formula:

Orange Dye, 0.1. 48035, having the formula:

4 Astraphloxine FF, C.I. 48070, having the formula.

H Hi): -c o The chromate coated pieces having the lake-forming substrate uniformly dispersed throughout the coating is rinsed with cold water and then entered into a dye bath containing say about 0.1% to 1% of the cationic dyestufi. The amount of such dyestulf will, of course, depend on the shade desired. The pH of the bath is adjusted to between about 3 and 4, preferably by the addition of acetic acid. The dyeing is elfected at a temperature of from about 50 F. to the boiling point of the dye bath, preferably at a temperature of about 90 F. say for about 5 to 15 minutes, the dyed piece removed and Washed. Below about 50 F., the rate of exhaust of the dyebath is so slow as to be undesirable.

The lake-forming substrate uniformly dispersed throughout the chromate coating, having been formed in situ as the coating is applied to the piece, reacts with the dye to form an insoluble lake which is therefore uniformly distributed throughout and on the chromate coating. Uniform, deep shades are thus produced, and this without deleteriously aifecting the wear and corrosion resistant properties of the chromate coating.

While the reasons for the present process succeeding in dyeing chromate coatings on aluminum or its alloys in deep shades without deleteriously affecting the wear and corrosion resistance of such coatings, are not fully understood, it is believed that the acid groups of the lakeforming substrate uniformly dispersed throughout the chromate coating, having been produced in situ in the chromate coating, react with the basic radicals of the cationic dyestulf to form insoluble color lakes. Thus the insoluble color lakes thus formed are integral with the chromate coating and uniformly dispersed thereon and therethroughout, resulting in uniform, deep shades. It will be understood the present invention is not to be limited to the above explanation.

The following examples are given for the purpose of illustrating the invention. It will be understood that the invention is not limited to these examples.

EXAMPLE I An aluminum panel measuring 2 inches by 4 inches by 0.016 inch is degreased by wiping with toluene. The panel is then immersed in a cleaning bath consisting of 100 cc. of 85% phosphoric acid, 10 cc. of a proprietary brightener (ARP #2, a product of Allied Research Products) and 890 cc. of distilled water. The cleaning bath is maintained at 90 F. The panel is removed after 3 minutes treatment in the bath and rinsed with cold water. The clean panel is coated with a chromate coating having uniformly dispersed therethroughout, phosphotungstic acid as the lake-forming substrate, by immersing in a solution consisting of 21 grams of an acid solution of chromate, fluorides and ferrocyanides (a commercial chromating preparation sold under the trade name Iridite #14 by Allied Research Products, disclosed in its US. Patent 2,796,371), 2 grams of phosphotungstic acid and 1000 cc. distilled water. This solution has a pH of 1.7. The coating is eifected by immersing the clean panel in the solution at F., maintaining it therein for 5 minutes, removing the panel and rinsing the coated panel with distilled water. The chromate coated panel is then dyed by immersion for 10 minutes in a dye bath at 90 F. consisting of 2 grams of Victoria Green WB Powder and 1000 cc. distilled water. The pH of the dye bath is adjusted to between 3.5 and 4.0 by addition of glacial acetic acid. The dyed panel is rinsed with water, dried in air and buffed by hand. lthas a uniform deep green shade good wear and corrosion. resistant prop- EXAMPLE-'11 This example fo'lltwvs the same-procedure as in Example I, but fflIVOlVeSfi-hC nse ofthefiyestufi5m9diin Table I in the same amount, instead of theVictoria Green (Cationic dyestufi disclosed in Ex. 4 of United States Patent 2,716,655).

In every case, the panel is uniformly colored the shade indicated and the colored chromate coating has good wear and corrosion resistance.

EXAMPLE III This example follows the procedure described in Example I in all details except that in the chromium coating step, instead of the phosphotungstic acid, the following lake-forming substrates are used in amount of about 1% by weight of chromating bath: phosphomolybdic acid, phosphotungstic-molybdic acid mixture, tannin and sulfonated naphthalene condensate (Naccotan A). The dyed panels are similar in all respects to that produced in Example 1.

EXAMPLE IV An aluminum panel of the same dimensions as used in Example I is degreased by wiping with toluene and then brightened by dipping for 30 seconds in a bath consisting of 70% nitric acid and 30% water. The panel is then rinsed with cold water and immersed for five minutes in a cleaning bath containing 683 grams sodium metasilicate, 225 cc. of keryl benzene sodium sulfonate (Nacconol SL) diluted to 13 gallons with water and maintained at 150 F.

The clean panel is then rinsed with cold water and immersed for five minutes in a chromate containing solution consisting of 24 grams potassium ferrocyanide, 5 grams sodium fluoride, 6.8 grams chromic oxide (CrO grams phosphotungstic acid diluted to 1 liter and maintained at 90 F. The pH of the chromate coating solution is 5.5 Upon removal of the chromate coated panel, it is rinsed with cold water and dyed by immersion in a dye bath at 90 F. containing 2 grams per liter of water of the yellow dyestuif, 0.1. 48055, having the formula:

C-CH1 0 CH:

o'f dyeina m es a e .ai an m minum allows producing -in which ble lake of the dye is uniformly distributed throughout the chromatepoating-due tokeaction cationic dye and the lake-forming substrate produced in situ in the chromate coating and thus uniformly distributed throughiourthis; ccatingr 'ihe resulting colored alumifminiflagd aluminum alloys are 'deeper'in shade and more attractive than has heretofore been obtainable on chemical coated aluminum or aluminum alloys. I

Since certain changes may be made in carrying out the above-described procedure for producing colored chemical conversion coatings or aluminum and/or its alloys and in the resultant colored aluminum and aluminum alloys without departing from the scope of this invention, it is intended that all matter contained in the above specification shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The process of forming a colored layer on the surface of a metal from the group consisting of aluminum and its alloys, which process comprises treating the aluminum with a chromate coating solution containing a lake-forming substrate to form a chromate layer thereon and thereafter dyeing said layer with a cationic dye to form a water-insoluble lake with the lake-forming substrate integral with said layer.

2. The process of forming a colored layer on the surface of a metal from the group consisting of aluminum and its alloys, which process comprises forming a chromate coating on said metal containing a lake-forming substrate uniformly distributed thereon and therethroughout and thereafter contacting the chromate coated metal with a cationic dyestufi which forms a water-insoluble lake with the lake-forming substrate integral with said coating.

3. The process of forming a colored layer on the surface of a metal from the group consisting of aluminum and its alloys, which process comprises treating the metal with an acidic solution containing chromium ion and a lake-forming substrate, forming a chromate coating having uniformly distributed thereon and therethroughout said lake forming substrate and thereafter contacting the chromate coating with a cationic dyestuif which forms a water-insoluble lake with the lake-forming substrate integral with said coating.

4. The process of forming a colored layer on the surface of a metal from the group consisting of aluminum and its alloys, which process comprises treating the metal with a chromating solution containing as its essential constituents a ferrocyanide, a fluoride, chromic oxide and a lake-forming substrate to form a chromate coating having the lake-forming substrate uniformly distributed thereon and therethroughout and thereafter contacting the chromate coating with a cationic dyestufi which forms a water-insoluble lake with the lake-forming substrate integral with said coating.

5. The process as defined in claim 4, in which from about 0.1% to about 5% by weight of the lake-forming substrate is present in the chromating solution applied to the metal.

6. The process as defined in claim 5, in which the lake-forming substrate is from the group consisting of phosphotungstic and phosphomolybdic acids, tannin, sulfonated naphthalene condensate, tartar-emetic, rosin soap precipitants, condensation products of trichlorobenzyl chloride and sulfonated phenol, formaldehyde naphthalene sulfonic acid condensation products and mixtures thereof.

7. A metal from the group consisting of aluminum and its alloys having thereon a chromate coating and an integral water-insoluble lake uniformly distributed thereon and therethroughout, said insoluble lake being pro duced by the reaction of a lake-forming substrate uniformly distributed on and throughout said chromate 7 8 coating with a cationic dyestufi which fom ns said insolw FOREIGN PATENTS P lake with the lake-firming substraw- 387,806 Gi'eat Britain Feb; 16, 1933 References Cite-d in the file of this patent. 489 14 Gre t Britain J ly 29.1938 UNITED STATES PATENTS Y 5 9 7 OTHER REFERENCES 9 2,030,236 Anderau Feb. 11, 1936 Light Metals, October 1949, pp. 536-541.

2,7Q6,371 Ostrander June 18, 1957 

1. THE PROCESS OF FORMING A COLORED LAYER ON THE SURFACE OF A METAL FROM THE GROUP CONSISTING OF ALUMINUM AND ITS ALLOYS, WHICH PROCESS COMPRISES TREATING THE ALUMINUM WITH A CHROMATE COATING SOLUTION CONTAINING A LAKE-FORMING SUBSTRATE TO FORM A CHROMATE LAYER THEREON AND THEREAFTER DYEING SAID LAYER WITH A CATIONIC DYE TO FORM A WATER-INSOLUBLE LAKE WITH THE LAKE-FORMING SUBSTRATE INTEGRAL WITH SAID LAYER. 